The present invention relates to a high frequency oscillator which is used in various communication equipments, measuring instruments, and the like.
A Colpitts oscillator is often used as a high frequency oscillator. A microstrip line resonator is used as an inductive element because of its low-loss characteristic.
The microstrip line resonator is also frequently used in a voltage controlled oscillator and the like. For example, a capacitor is connected to an open end of the microstrip resonance line, a DC circuit consisting of a DC blocking capacitor and a variable capacitance diode is connected to the other end, and a control signal of the oscillating frequency is applied to the central connection point of the DC blocking capacitor and variable capacitance diode. The voltage controlled oscillator of such a constitution is frequently used as a voltage controlled oscillator (VCO) of a local oscillator, a frequency synthesizer, or the like of a UHF tuner. However, such a VCO has drawbacks such that the unloaded Q of the resonator is not high, spatial separation between the resonator and the other circuits is bad, stray coupling occurs, the stability of the oscillator is low, and the like.
As a resonator having a high Q and using a strip line, a ring resonator is disclosed in and known from Japanese Patent Examined Publication No. 42574/1979 which corresponds to U.S. Pat. No. 4,121,182 granted Oct. 17th, 1978 to Makimoto et al. Although the resonator is used as, e.g., an element of a filter, it is not used as a resonance element of an oscillator.